spi: hisi-kunpeng: Add validation for the minimum value of speed_hz

The speed specified by the user is used to calculate the clk_div based
on the max_speed_hz in hisi_calc_effective_speed.  A very low speed
value can lead to a clk_div larger than the variable range. Avoid this
by setting the min_speed_hz so that such a small speed value is
rejected.  __spi_validate() in spi.c will return -EINVAL for the
specified speed_hz lower than min_speed_hz.
Signed-off-by: Devyn Liu <liudingyuan@huawei.com>
Reviewed-by: Jay Fang <f.fangjian@huawei.com>
Link: https://patch.msgid.link/20240730032040.3156393-2-liudingyuan@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-hisi-kunpeng.c

@@ -495,6 +495,7 @@ static int hisi_spi_probe(struct platform_device *pdev)
 	host->transfer_one = hisi_spi_transfer_one;
 	host->handle_err = hisi_spi_handle_err;
 	host->dev.fwnode = dev->fwnode;
+	host->min_speed_hz = DIV_ROUND_UP(host->max_speed_hz, CLK_DIV_MAX);
 
 	hisi_spi_hw_init(hs);